The present invention generally relates to cooling systems, and more particularly to systems that include both air and vapor cycle cooling systems.
Future military aircraft will require greatly advanced capabilities in order to ensure air superiority, survival in heavily defended airspace, and success against a wide range of potential targets. These capabilities, including electronic attack and directed energy weapons, are expected to require as much as 10 times higher electric power levels than existing weapon systems.
While these power demands are significant, thermal management of these advanced systems will present an even greater challenge, due to low component efficiencies and waste heat quality. Low-observability requirements, such as limitations on ram air availability, composite aircraft skins which inhibit heat transfer, and higher efficiency engines with less fuel flow available for cooling, further compound this challenge.
Air cycle systems (ACS) offer the potential advantage of high pressure ratios and lift temperatures, and thus can be used with hotter heat sinks than comparable vapor cycle systems (VCS). However, ACS are much less efficient than VCS, resulting in higher power requirements and higher heat rejection demands.
On the other hand, VCS systems are more efficient, but require lower heat sink temperatures that are often not available without a dedicated ram air source, which still may be too hot to use during high speed flight.
Further, for the large thermal loads anticipated, the cooling system itself will require substantial power to drive it. The use of electric power would further tax the vehicle's electric power generation capability and the power conditioning, motor controllers, and motors needed would be relatively heavy, expensive, and unreliable. A direct mechanical drive may also be problematic as engines are not currently equipped for such high power take-off shaft loads, and incorporating such into new engine designs involves a number of design compromises including added weight, cost and mechanical complexity.
As can be seen, there is a need for an efficient cooling system that can be used in aircraft environments of the type described.